In order to acquire a better understanding of the mechanism chemical carcinogenesis, we have initiated studies on the conformation of DNA and RNA in solution and their interactions with carcinogens and mutagens. The methods employed in these studies include nuclear magnetic resonance (NMR), circular dichroism (CD), electric linear dichroism, organic synthesis of DNA and potential energy calculations. Specific topics included in this project are: (1) studies on the interactions between the tryptophan pyrolysates Trp-P-1 and Trp-P-2, with dinucleoside phosphates CpG, GpC, UpA, ApU, dCpdG, dGpdC, dTpdA and dApdT. The capacity of these compounds to form nucleotide complexes differ in that Trp-P-1 was more effective than Trp-P-2. Also, the complex formation was more extensive with ribonucleotides than deoxyribonucleotides and with pyrimidine-purine sequence as compared to purine-pyrimidine sequences. (2) Studies on the effects of 5-methyl cytosine on the conformation of dinucleotides. It was found that the 5-methyl group in cytosine enhances base pair formation with guanine and stabilizes the base pair. (3) Studies on the solution conformation of trinucleotide diphosphates (trimers). We found the trimers assume the four stable conformations of dinucleoside phosphates. In addition, they also exhibit "bulged" structure with the bases of the two terminal residues stacking on each other and the middle residue sticking out of the stack. This bulged conformation is proposed as the structural model for frame-shift mutation. (4) Studies on the solution conformation of 1-nitroso-cis-2,6-piperidine dicarboxylic acid. It has rigid half-chair conformation in pyridine as well as in water solution, corresponding to the crystal structure of this compound. Change in pH induced distinct change of the 1-nitroso-cis-2,6-piperidine dicarboxylic acid structure from one rigid state to another rigid state.